Sanaa, Yemen—A boy rinses a bucket after collecting water from a well allegedly contaminated with cholera bacteria on July 12. In June, the U.N. health agency said Yemen was facing “the worst cholera outbreak in the world” and more than 300,000 people have been infected in the past few months. In July, U.N. officials said plans to ship as many as 1 million doses of cholera vaccines to Yemen would likely be suspended over security concerns. Two years of conflict between government forces and separatist rebels has created a public health crisis and made it impossible for millions to access safe drinking water.